The design of athletic shoes is becoming increasing important to the performance of athletes. As athletic events become more competitive, small improvements in performance become increasingly significant. Athletic shoes that enhance the performance of athletes by only a few tenths or hundredths of a second, or a fraction of a centimeter, can provide the xe2x80x9cwinning edgexe2x80x9d sought by athletes. For this reason, athletes are constantly seeking shoes that improves their performance.
Many features have been added to athletic shoes to increase athletic performance. Most such improvements have been made in the physical and structural composition of the interior and exterior elements of soles of athletic shoes. Other improvements include increasing the amount of cushioning or shock absorption to prevent injury to the wearer. Such improvements are often made at the expense of energy return, so that the shoe may actually decrease athletic performance.
The material most frequently used for insoles in athletic shoes is ethylene vinyl acetate (xe2x80x9cEVAxe2x80x9d). EVA is a lightweight, inexpensive, sponge-like material that does not provide significant energy return to the wearer. Examples of shoe insoles made from EVA are disclosed in a U.S. patent to Fujita et al. (U.S. Pat. No. 4,418,483), which is incorporated herein by reference. This patent teaches making shoe midsoles by combining EVA with a styrene-butadiene rubber. While such midsoles have excellent cushioning properties, they do not enhance athletic performance by providing significant energy return to the user. Rather, the cushioning effect of EVA reduces performance by absorbing energy.
Fujita et al. also disclose a shoe soles or midsoles of 1,4-polybutadiene with other rubbers, such a 1,2-polybutadiene. These other rubbers do not provide substantial energy return, and can actually reduce energy return provided by the 1,4-polybutadiene. For example, in its cured state, 1,2-polybutadiene is a hard material which lacks the ability to be compressed and rebound to provide energy return. In its uncured state, 1,2-polybutadiene (syndiotactic) exhibits mild elastomeric properties. When high energy return rubbers such as 1,4-polybutadiene rubber are combined with 1,2-polybutadiene, the 1,2-polybutadiene typically controls the characteristics of the resulting composition and reduces its energy return. Similarly, Fujita et al. teach the inclusion of fillers such as hard clay and silica, which also reduce the energy return of the shoes.
A U.S. patent to S. P. Chang and R. I. Chang (U.S. Pat. No. 5,147,589), which is incorporated herein by reference, discloses a method of making shoe soles of a polymer blend which is a mixture of rubbers including thermoplastic elastomers, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and plastics such as polystyrene, EVA, or polyvinyl chloride. When high energy return rubbers such as 1,4-polybutadiene are incorporated into such shoe soles, the high energy return rubbers compose only a small weight percentage of the total rubber in the shoe, and, therefore, the shoes do not provide substantial energy return. Chang et al. also teach the inclusion of non-energy returning materials (xe2x80x9cfillersxe2x80x9d), including white hard clay, white carbon VN-3 filler, carbonates and silica. These materials modify some characteristics of the soles, such as durability or strength, of the shoe part, but also decrease energy return
A U.S. patent to T. Noyama and A. Nakahara (U.S. Pat. No. 5,288,446) discloses a process for imparting strength to rubber articles. This patent is incorporated by reference herein. Noyama et al. teach enhanced strength by adding fillers such as metal salts of alpha, beta-unsaturated fatty acids, nylon and calcium carbonate. Such fillers harden the rubber article and improve its strength at the expense of energy return. Because such hardened compositions are less compressible, they can also injure the user.
A U.S. patent to Sullivan et al. (U.S. Pat. No. 4,910,886) discloses a shoe insert for total shock absorption, but not for energy return. This patent is incorporated by reference herein. The innersole of Sullivan et aL contains predominant amounts of a substantially non-deformable, expandable polymer, such as elastomeric urethane. Such materials are not known for providing energy return or for improving athletic performance.
While the energy return of 1,4-polybutadiene, in the form of super balls, for example, is known, those of ordinary skill in the shoe art have not looked to shoe components made of 1,4-polybutadiene and other high energy return rubbers to improve athletic performance. The manufacturers of athletic shoes have failed to appreciate that significant energy return is available from shoe components of 1,4-polybutadiene alone or in combination with another high energy return rubbers such as natural rubber, synthetic isoprene rubber, polyisoprene, butadiene acrylonitrile rubber or ethylenepropylene diene modified rubber.
The present invention provides a shoe component comprising 1,4-polybutadiene. The 1,4-polybutadiene can be combined with other high energy return rubbers, such as natural rubber, synthetic isoprene rubber, polyisoprene, butadiene acrylonitrile rubber or ethylenepropylene diene modified rubber. The shoe component is typically substantially free of fillers that reduce the energy return of the component. The shoe component is preferably placed in a shoe between the user""s foot and the shoe sole. Thus, the shoe component can be, for example, an insole, midsole, or shoe insert, or a portion of an insole, midsole or shoe insert. The shoe component is compatible with use in a wide variety of shoes, including, but not limited to, athletic shoes, dress shoes, casual shoes, walking shoes, sandals, and the like. The shoe components can also be shaped to fit a variety of shoes and can be positioned within the sole, at the midsole, at the insole, or on top of the insole.
Methods of making and using the invented shoe components are also provided. In one embodiment, when the shoe component is inserted into an athletic shoe, the shoe component can increase the ability of the wearer to leap forward, jump upward, and/or run faster, and the like. Suitable activities (e.g., exercises) in which performance is improved include walking, running, weight lifting, broad jumping, high jumping, volleyball, basketball, football, soccer, and the like. In another embodiment, the shoe component increases the wearer""s strength. In still another embodiment, the shoe component improves the performance of the wearer""s heart, such as by reducing fibrillation. In yet another embodiment, the shoe component provides a resilient, high energy return material that reduces injury.